The present invention relates to body insertable prosthetic devices designed to maintain openings for ventilation, drainage of fluids and delivery of medications, and more particularly to prostheses designed to promote tissue healing while maintaining patency of a lumen surrounded by the healing tissue.
Otitis media, inflammation of the middle ear, is one of the most common childhood diseases. This condition frequently involves a build up of fluid in the middle ear, known as otitis media with effusion (OME), estimated to affect over two million individuals each year. The fluid accumulation applies pressure to the tympanic membrane (eardrum) that can be painful and can lead to hearing loss, interfere with speech and language development, and damage the tympanic membrane and other middle ear structures.
The most common surgical treatment of this condition, known as a myringotomy, involves forming an incision through the tympanic membrane, followed by insertion of a PE (pressure equalization) tube into the incision. As the tympanic membrane heals around the tube, a lumen through the tube remains patent to enable fluid drainage and ventilate the middle ear space. PE tubes are also placed to facilitate delivery of medications to the middle ear to treat such disorders as sudden hearing loss and Meniere's Disease.
In other sites, e.g. the paranasal sinuses, a similar tubular prosthesis structure with a lumen can be used to drain fluid from a sinus or to irrigate a sinus while providing a stent to prevent narrowing of the passage. Present sinus stents are non-biodegradable and require removal either in a second operative setting or in a clinic, with significant discomfort to the patients.
A variety of PE tubes have been developed over the years. Examples are seen in U.S. Pat. No. 4,468,218 (Armstrong), U.S. Pat. No. 5,053,040 (Goldsmith III), U.S. Pat. No. 7,097,661 (Perry), and in published international application, Publication No. WO 2008/036368 (Cottler). The tubes are formed from a variety of body compatible materials including polytetrafluoroethylene (PTFE) and other suitable fluoroplastics, silicone, gold, titanium, and their alloys. A typical tube includes an elongate shaft or tube designed to reside in the tympanic membrane incision, and opposite end flanges, each with a diameter larger than the shaft diameter. The flanges are adapted for location on opposite sides of the tympanic membrane to more positively secure the shaft in the incision. Alternative designs employ only one flange at the inner or distal end of the shaft for placement against the medial side of the tympanic membrane.
One problem with this type of ventilation tube is the lack of control over the length of time the tube remains in place. The tubes are subject to spontaneous extrusion from the tympanic membrane. Premature loss of the tube in this fashion results in the need for further surgery to replace the tube. The medial side flanges can be enlarged or otherwise configured to counteract the spontaneous extrusion tendency. This, however, increases the difficulty of initial insertion through the incision, and increases the difficulty of removing the tube after it is no longer needed. Thus, the lack of control can involve either a premature spontaneous extrusion or an undesirable tendency to remain in place beyond the time needed for treatment.
Another problem with the conventional ventilation tube is the risk of a persistent perforation of the tympanic membrane once the tube has extruded. Although this problem arises in just a small percentage of procedures, it underscores the need for promoting tissue healing and closure of the incision.
It has been proposed to eliminate the need for removal by forming the tube of a biodegradable material. U.S. Pat. No. 4,650,488 (Bays) discloses a prosthesis in which polymers of lactic acid, e.g. poly (DL-lactide), are used to form the entire ventilation tube, or at least the shaft plus the medial flange. The shaft is tapered, diminishing in diameter in the inward direction, so that once the shaft dissolves, the medial flange falls into the middle ear and the lateral flange falls outward into the external ear canal. Bays notes that degradation time can be varied through material selection, radiation, and size.
U.S. Pat. No. 7,163,557 (D'Eredita) discloses a biodegradable prosthesis formed of resorbable polyphosphazenes. Like Bays, D'Eredita mentions radiation as a means to increase the speed of degradation, and notes a preference for dissolving the central body or shaft before the flanges.
U.S. Pat. No. 6,379,323 (Patterson) is directed to a myringotomy tube formed of gelatin, more particularly as sold under the brand name GELFILM. Patterson advises that the gelatin shaft of the tube tends to loose its lumen patency and collapse upon itself if the internal diameter is not made large enough, specifically at least about 2.0 mm.
Although the biodegradable prostheses can eliminate the need for surgical removal of ventilation tubes, they encounter difficulties in simultaneously addressing essential and desirable prosthesis features which compete with one another. For example, in many applications it is necessary for the prosthesis to maintain its structural integrity in situ for several weeks or more, especially in terms of maintaining lumen patency for better fluid drainage and ventilation. This suggests the need for a relatively large size and relatively slow resorption or degradation rate. Conversely, the need to promote the healing of tissue and closure of the incision suggest the need for a smaller size and higher degradation rate. The hemostatic function of the prosthesis indicates the need for a porous, absorbent structure, while a smoother, less porous structure would provide more effective drainage of fluids from the middle ear.
In addition, the biodegradable prostheses disclosed to date do not adequately address the need to promote tissue healing and closure of the incision. The D'Eredita patent includes material critical of polylactides, contending that they involve the risk of growth of granulation tissues consequent upon their imperfect absorption by the tissues, and does not address the need for hemostatic properties.
Accordingly, the present invention has several aspects, each directed to one or more of the following objects:                to provide a tubular prosthesis resorbable in situ in a manner that more reliably maintains patency of a lumen through a tube, and promotes healing of surrounding tissue for closure of an incision or perforation through which the tube extends;        to provide a resorbable tympanic membrane prosthesis with hemostatic properties and porocity at least throughout its radially outward regions to enhance its function as a hemostatic device;        to provide a composite tubular prosthesis with a resorbable tubular inner layer with a smooth lumen wall for enhanced flow of fluids through the lumen, combined with a coaxial outer layer with a higher porocity and higher resorbtion rate; and        to provide a structurally self-supporting body absorbable prosthesis that advantageously incorporates denatured gelatin sponge material to promote healing and closure of an opening in tissue through which the prosthesis extends.        